The most common locations at which prosthetic heart valves are implanted are the aortic and mitral valves associated with the left ventricle, which generates the higher pressures of the two ventricles. The anatomy of the aortic and mitral valves are quite different, with the former being a tri-symmetric/tri-leaflet structure, and the latter having two dissimilar leaflets. The aortic annulus defines an undulating fibrous structure around substantially a circular ring to support the up-and-down shape of the cusps and commissures of the native leaflets. On the other hand, the mitral annulus has a somewhat fibrous linear anterior aspect across the septum of the heart from the aortic valve, but the posterior aspect, which defines the majority of the annulus, is relatively less fibrous and more muscular. Also, the posterior aspect is nearly oval-shaped such that the mitral annulus presents a malformed “D” shape. The present invention is directed to prosthetic heart valves particularly suited for implant at the mitral annulus.
The left ventricle LV and valves associated therewith are depicted in FIG. 1 as seen in vertical cross-section along an anterior-posterior plane. The mitral valve MV controls flow from the left atrium LA to the left ventricle LV, while the aortic valve AV functions between the left ventricle LV and ascending aorta AA. Both the mitral valve and aortic valve include leaflets that extend into the blood flow path and are supported around their peripheries by respective fibrous annuluses. For purpose of discussion, the mitral annulus of a normal, healthy heart lies generally in a mitral annulus plane MAP defined perpendicular to the average blood flow direction 20 (see FIG. 1) through the mitral valve MV. Although a typical mitral annulus may be three-dimensional, the mitral annulus plane MAP will be used as a reference plane that extends through the posterior aspect of the annulus. Papillary muscles are not shown but attach to the lower portion of the interior wall of the left ventricle LV and chordae tendineae extend between and link the papillary muscles and free edges of the anterior and posterior leaflets.
FIG. 2 illustrates in plan view the mitral valve MV from the left atrium as exposed during surgery, while FIG. 2A schematically identifies the commonly identified features. The anterior aspect of the mitral annulus forms a part of the “cardiac skeleton” and includes anteriolateral ALT and posteriomedial PMT fibrous trigones. The mitral valve MV is a bicuspid valve having a posterior leaflet (separated into three cusps P1, P2, P3) that cooperates or coapts with an anterior leaflet A. The anteriolateral ALT and posteriomedial PMT trigones are indicated at the junctions between the anterior leaflet A, and the first and third cusps of the posterior leaflet P1, P3, respectively. The trigones are also sometimes known as commissures.
As mentioned above, and with reference to FIG. 2A, the mitral annulus has a malformed “D” shape in plan view with the straight portion, or anterior aspect, extending between the anteriolateral ALT and posteriomedial PMT trigones. The longest dimension of the mitral annulus defines a major axis 22 while the shortest dimension defines a perpendicular minor axis 24. The minor axis 24 generally bisects the anterior leaflet A. Although the mitral annulus is not circular, a center 26 thereof can be defined at the intersection of the major and minor axes 22, 24. Radial lines can be drawn outward from this imaginary center 26 through the anteriolateral ALT and posteriomedial PMT trigones to indicate the angular separation φ therebetween. This angular separation φ varies from patient to patient, but is generally about one-third of the circumference around the mitral annulus, or between 120°-125°.
Two primary types of heart valve replacements or prostheses are known: rigid leaflet or ball-type mechanical valves, and “bioprosthetic” valves having flexible leaflets supported by a peripheral frame. The flexible leaflets of bioprosthetic valves project into the flow stream and function much like those of a natural human heart valve, imitating their natural flexing action to coapt against each other and ensure one-way blood flow. In tissue-type valves, a whole xenograft valve (e.g., porcine) or a plurality of xenograft leaflets (e.g., bovine pericardium) typically provide fluid occluding surfaces. Synthetic leaflets have been proposed, and thus the term “flexible leaflet valve” refers to both natural and artificial “tissue-type” valves. One example of a flexible leaflet valve is disclosed in U.S. Pat. No. 5,928,281 to Huynh, et al. (Edwards Lifesciences, Corp., Irvine, Calif.), the disclosure of which is hereby expressly incorporated by reference.
Bioprosthetic valves may be “stented,” wherein two or more flexible leaflets are mounted within a metallic or polymeric peripheral support frame that usually includes posts or commissures extending in the outflow direction to mimic natural fibrous commissures in the native annulus. The support frame includes an undulating outflow edge including alternating inflow cusps and outflow commissures. The commissures are often flexible and extend generally axially in the outflow direction in a cantilevered fashion so as to be fixed at the inflow end and be capable of flexing along their lengths and distributing the forces associated with blood flow. One commonly used peripheral support frame is a flexible, undulating wire, sometimes called a “wireform,” which has a plurality (typically three) of large radius cusps supporting the cusp region of the flexible leaflets (i.e., either a whole xenograft valve or three separate leaflets). The ends of each pair of adjacent cusps converge somewhat asymptotically to form upstanding commissures that terminate in tips, each extending in the opposite direction as the arcuate cusps and having a relatively smaller radius. This provides an undulating reference shape to which a fixed edge of each leaflet attaches (via components such as fabric and sutures) much like the natural fibrous skeleton in the aortic annulus. One example of the construction of a flexible leaflet valve is seen in U.S. Pat. No. 5,928,281. Other “support frame” constructions exhibit sheet-like tubular shapes but still define undulating commissures and cusps on their outflow ends, such as shown in U.S. Pat. No. 5,984,973 to Gerard, et al. Components of the valve are typically assembled with one or more biocompatible fabric (e.g., Dacron) coverings, and a fabric-covered sewing ring is provided on the inflow end of the support frame.
Many other stented flexible leaflet valve configurations are known, including U.S. Pat. No. 6,086,612 to Jansen (Adiam Medizintechnik GmbH & Co. KG, Germany) which discloses a mitral valve prosthesis having a support housing with a large base ring (12) that bears two stays (18, 19) which substantially extend in the ring axis direction and are connected by curved walls for securing two flexible synthetic cusps (leaflets). The free ends of the stays form an inner support for the cusps. The base-ring has in the top view a closed, non-round shape with a common longitudinal axis (15) but two transverse half-axes (16, 17) of different sizes.
“Stentless” prosthetic valves have essentially no rigid elements coupled to the flexible leaflets and an annular support frame so as to limit movement constraints. An example of a stentless valve is seen in U.S. Pat. No. 5,415,667 to Frater. Frater discloses a four-leaflet mitral heart valve replacement of essentially flexible bioincorporable material. The valve includes a generally D-shaped (30) sewing ring having an opening (31) with a long straight side (32), a shorter side (35) opposite the longer side, and lateral sides of the opening (31) extending between adjacent ends of the long and short sides. An anterior cusp (33) hinges on the long side, a posterior cusp (34) hinges on the shorter side portion (35), and two lateral cusps (36A & 36B) hinges on each of the remaining sides. Chordae of bioincorporable material extend from edges of the cusps for connection to the papillary muscles in the cavity of the ventricle when the sewing ring is sutured to the atrio-ventricular junction of the patient's heart.
The Frater four-leaflet mitral valve design has been clinically investigated as the quadrileaflet mitral valve (SJM-Quattro-MV). The SJM-Quattro-MV is a stentless bioprosthesis made of bovine pericardium with standard glutaraldehyde tanning and additional anticalcification treatment with polyol. The valve consists of a large anterior and posterior leaflet and two small commissural cusps. The leaflets have straight hinge lines to avoid the excessive flexion stress of stented prostheses. The annulus is made of a three-layer pericardium and serves as a flexible annuloplasty device as well. Chordal support consists of two papillary flaps that support the anterior and posterior cusps.
Numerous prosthetic mitral heart valves have been proposed in the art, typically without too much consideration of the unique attributes of the mitral annulus. In particular, they have been no commercially successful attempts to modify conventional prosthetic valves to better conform to the mitral annulus.